Surface treatment of uranium



Sept. 23, 1958 o. FLl 2,853,441

SURFACE TREATMENT or mama Filed Sept. 29, I949 OLIVER FLINT Inventor y MB w assignments, to the United States of America as represented by theUnited States Atomic Energy Commission Application September 29, 1949,Serial No. 118,630

' 15 Claims. cram-1.5

This invention relates to thesurface treatment of bodies of uranium oruranium-rich alloy.

An object of the invention is to provide a method of treating suchbodies whereby to produce a bright lustrous finish which shows little or.no change on exposure to-air for substantially 3 hours and which mayserve as a basis for electroplating, coating by dipping, or the like.

A further object of the invention is to provide a method treating bodiesof uranium or uranium-rich alloy which have become coated with oxide, inparticular black oxide layers, whereby to remove or reduce the oxide,substantially' without loss of the metal carrying the coating.

In accordance with theinvention, the surface of a body of uranium oruranium-rich alloy, which is substantially free from black oxidecoating, is given abright lustrous finish by anodic electrolytictreatment in a solution of-a weak organic acid, particularly ahydroxypolycarboxylic acid or a polycarboxylic acid. Examples of acidwhich may be employed are citric acid, tartaric acid, oxalic acid.Citric acid is the preferred organic acid. Tartaric acid is somewhatslower in operation'than citric acid and with oxalic acid, there is atendency for basic uranium oxalates to precipitate. The treatment ispreferably carried out at ordinary temperature employing a low currentdensity at the anode,vfor example 3 amperes per square foot.Concentrations of 1 to percent by weight or more of the organic acid inwater may be employed.

The bright silvery finish which is produced in this manner has beenfound. to be. stable in air forperiods of 3 hours and to form asatisfactory basis for electroplating on the uranium or uranium alloy,and for coatings produced by dipping into molten metal baths. Objectsprovided with the finish may also be subjected to controlled oxidationto produce desired oxide coatings.

Uranium or. uranium-rich alloy having black oxide coating, may berendered suitable for treatment accordingto.

the invention by a preliminary anodic electrolytic treatment in analkaline solution preferably at elevated temperature. An aqueous sodiumcarbonate solution constitutes a preferred electrolyte for1use in; thisaspect of the invention, and by its use removal of the blackpxide iseffected. A further preferred electrolyte is an aqueQus solutionof'sodium hydroxide partially neutralis'ed'by citric acid, oralternatively a solution of sodium hydroxide to which has been addedsodium citrate, the use of either of which results in conversion ofblack oxide coatings into brown hydroxide which is removed by anodicelectrolytic treatment in solution of citric acid. Preferred anodiccurrent densities for use with these electrolytes are approximately 60ampere per square foot.

Uranium bars having surface contamination of electrically conductingparticles, especially graphite, when treated according to the inventionhave frequently been found to develop surface pits, presumably owing tolocal action between the particles and uranium accelerated by theconditions of the treatment. Such pitting has been avoided by suspendingbars of uranium having such con- 2,853,441 Patented Sept. 23, 1958tamination in 10 percent aqueous sodium carbonate solution at 100 C. forfifteen minutes prior to treatment according to the invention, wherebythe contaminating particleswere loosened'and weresubsequently washed offin running water. Oxide scale on the uranium-bar was then removed, andabright finish applied in the manner set out above.

The presence of halides has a disturbing effect on the treatment of theinvention, owing it is believed, to halides accelerating acceleratingthe rate of'oxidation. They should therefore be removed beforetreatment. A pretreatment in hot water-has been found to be effective-inremoving barium chloride. Thus uranium bars-wereimmersed in boilingwater for 30 minutes, rinsed in cold water and immersed'ina freshbath'of boiling water for a further- 30 minutes, after which a finalrinsing incold water was given before treatment according to theinvention.

The following are examples of preferred ways of-carrying the inventionintoefiect.

Example .1

A cylindrical barofuranium-which' had a heavy' black oxide coatingformed thereon and carried brazing'scale and inorganic contamination wasdegreased-in acetone, clipped into a mild steel supporting rack andsuspended in an electrolyte consisting of a 10 percent aqueoussodiumcarbonate solution maintained at C.

The supporting rack employed isillustrated in the accompaniyng drawing.It is formed from a round her of steel 1, one end of which hasbeen-ground or machined to a point 5. The bar is' bent as shownandprovidedwith a tapped hole 6 receiving the set screw-3=which is alsoprovided with apoint 4. The position'of the hole-6 is such that its axisis in the line of point 5. The handle portion 2 may be provided with arubber or the like grip. The bar of uranium to be'treated is provided atthe center of each end with a depression for engagement by the points 4ands of the supporting rack, the screw 3 being tightened to hold therod.

Using mild steel cathodes, the'bar was subjectedto anodic electrolytetreatment for approximately 10 minutes with acurrent density of 60amperesrpersquarefoot. All oxide, scale andinorganic contamination wasremoved from the bar by the treatment.

The bar was then removed from the electrolyte, rinsed in cold water andimmersed in an electrolyte consistingot 10 percent aqueous citric acidsolution at ordinary temperature, in which it was made anode to a,graphite electrode. Ananode current density of 3 amperes per square footwas maintained for one minute, after which' the bar was removed, washedwith cold water and'dried'with acetone. Abright silvery finish wasobtained.

When the cleaned bar was removed from the first electrolytic bath -agolden oxidefilm formed on the cleaned surface,- but the film wasremoved by the treatment in th'e citric-acid bath; V

Example 2 A uranium bar similar to that used in Example -1 was degreasedin acetone and then suspended in an electrolyte consisting of an aqueoussolution containing 20 percent sodium hydroxide and 7.5 percent citricacid. Using a mild steel cathode and an anodic current density of 60amperes per square foot and an electrolyte temperature of 80 C., the barwas subjected to anodic electrolytic treatment for 30 minutes, by whichtreatment the black oxide coating was converted to brown hydroxide. Thebar was removed from the electrolyte rinsed in cold water and made anodeto graphite in a 10 percent aqueous citric acid electrolyte as inExample 1. The brown hydroxide layer was removed by the treatment in thecitric acid-containing electrolyte and a bright silvery finish wasobtained. The bar was finally washed in water and dried with acetone.

Example 3 A uranium bar which had been treated in a percent aqueoussodium carbonate solution as described in Example 1 to remove oxide andscale was rinsed in cold water and immersed in an electrolyte consistingof a 10 percent aqueous tartaric acid solution at ordinary temperature.It was made anode to a graphite electrode, and current was passed forone minute employing an anode current density of amp. per sq. ft. Thebar was then removed, washed with cold water and dried with acetone. Abright clean surface resulted.

By the expression uranium-rich alloy employed in the presentspecification is meant an alloy containing at least 97 percent by weightof uranium. The term polycarboxylic'acid means an acid containing morethan one carboxyl group.

I claim:

;l. A method of producing a bright lustrous finish on surfaces of bodiesof uranium and uranium-rich alloy, wherein the surface is caused toundergo anodic electrolytic treatment in a solution of a weak organicacid -of the class consisting of hydroxy-polycarboxylic acids andpolycarboxylic acids.

2. A method of producing a bright lustrous finish on surfaces of bodiesof uranium and uranium-rich alloy, wherein the surface is caused toundergo anodic electrolytic treatment in a solution of citric acid.

3. A method according to claim 2 wherein an aqueous solution of from 1to 10 percent citric acid is employed.

4. A method according to claim 2 wherein a low anodic current density ofthe order of 3 amperes per square foot is employed.

5. A method of producing a bright lustrous finish on surfaces of bodiesof uranium and uranium-rich alloy, wherein the surface is caused toundergo anodic electrolytic treatment at ordinary temperature in anaqueous citric acid solution. 7 6. A method of producing a brightlustrous finish on surfaces of bodies of uranium and uranium-rich alloycarrying a black oxide coating, wherein the surface is caused to undergoanodic electrolytic treatment in an aqueous alkaline solution, and isthen caused to undergo anodic electrolytic treatment in a solution of aweak organic acid of the class consisting of hydroxy-polycarboxylicacids and polycarboxylic acids.

7. A method of producing a bright lustrous finish on surfaces of bodiesof uranium, and uranium-rich alloy carrying a black oxide coating,wherein the surface is made anode in an aqueous sodium carbonatesolution substantially to remove the said black oxide coating, and isthen made anode in a solution of a weak organic acid of the classconsisting of hydroxy-polycarboxylic acids and polycarboxylic acids.

8. A method of producing a bright lustrous finish on made anode in anaqueous sodium carbonate solution substantially to remove the said blackoxide coating and is then made anode in a solution of citric acid.

9. A method according to claim 8 wherein the said citric acid solutionin an aqueous solution of from 1 to 10 percent concentration.

10. A method according to claim 8 wherein the said citric acid solutionis an aqueous solution of from 1 to 10 percent by weight, and a currentdensity at the anode of the order of 3 amperes per square foot isemployed.

11. A method of producing a bright lustrous finish on surfaces of bodiesof uranium and uranium alloy carrying a black oxide coating, wherein thesurface is caused to undergo anodic electrolytic treatment at elevatedtemperature in an aqueous sodium carbonate solution for approximatelyten minutes substantially to remove the said oxide coating and is thencaused to undergo anodic electrolytic treatment in an aqueous citricacid solution of approximately 10 percent concentration at ordinarytemperature for approximately one minute.

12. A method according to claim 11 wherein the said first anodictreatment is carried out with a current density of approximately 60amperes per square foot of anode surface.

13. A method of producing a bright lustrous finish on a body of uraniumhaving a black oxide coating thereon, which comprises subjecting thebody to anodic electrolytic treatment for about 10 minutes in an aqueoussodium carbonate solution at 80 C. and an anode current density of 60amperes per square foot, rinsing the body and subjecting it to anodicelectrolytic treatment in a 10 percent aqueous citric acid solution forone minute at a current density of 3 amperes per square foot.

14. A method of producing a bright lustrous finish on a body of uraniumhaving a black oxide coating thereon which comprises subjecting the bodyto anodic electrolytic treatment for about 10 minutes in an aqueoussolution containing 20 percent sodium hydroxide and 7.5 percent citricacid employing an anodic current density of 60 amperes per square footand a temperature of 80 C., rinsing the body and subjecting it to anodicelectrolytic treatment in a 10 percent aqueous citric acid solution forone minute at a current density of 3 amperes per square foot of anode.

15. A method of producing a bright lustrous finish on a body of uraniumwhich comprises subjecting the body to anodic electrolytic treatment forabout 10 minutes in surfaces of bodies of uranium and uranium-rich alloycarrying a black oxide coating, wherein the surface is an aqueous sodiumcarbonate solution at C. and an anode current density of 60 amperes persquare foot, rinsing the body and subjecting it to anodic electrolytictreatment in a 10 percent aqueous tartaric acid solution for one minuteat an anode current density of 15 amperes per square foot.

References Cited in the file of this patent UNITED STATES PATENTS

2. A METHOD OF PRODUCING A BRIGHT LUSTROUS FINISH ON SURFACES OF BODIESOF URANIUM AND URANIUM-RICH ALLOY, WHEREIN THE SURFACE IS CAUSED TOUNDERGO ANODIC ELECTROLYTIC TREATMENT IN A SOLUTION OF CITRIC ACID.